Interleukin-20 (IL-20) is a recently discovered cytokine which bears significant homology to IL-10, IL-19 and IL-24. IL-20 was first identified in keratinocytes but its functions are still largely unknown. Transgenic mice over-expressing IL-20 exhibit a skin disorder very similar to psoriasis. In addition, the receptor for IL-20 is over expressed in human psoriasis, indicating that it is involved in the pathology of this common autoimmune disease. Phase II clinical trials are already underway using exogenous IL-10 to suppress autoimmunity in psoriasis patients. In contrast, IL-20 may enhance autoimmune responses in skin or directly influence keratinocyte growth in psoriatic lesions. In collaboration with Regeneron, we have developed an IL-20 knockout mouse* to test whether IL-20 is crucial for normal skin development and immune function. The initial aim of the pilot study will be to obtain data on the expression of IL-20 in mice using mRNA analysis, and the expression pattern of a LacZ gene knocked into the murine IL-20 sequence will be prepared and screened for use in western blot and FACS analysis. The data should validate our rationale for investigating the role of IL-20 in psoriasis and its potential as a novel target for therapy. *The IL-20 knock out mice to be used in these future experiments will be generated from IL-20 deficient embryonic stem cells provided by Regeneron Pharmaceuticals, Inc., subject to an in accordance with the terms of the Research Collaboration Agreement currently in effect between Dr. Richard Flavell, Yale University and Regeneron, on a nonexclusive basis as reasonably available for these studies.